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How powerful generator is needed for this PA system

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How powerful generator is needed for this PA system

Postby Marjan Dobelsek » Sun Aug 10, 2014 8:46 am

We're going to have an open-air gig where we'll have to use electrical generator to power up our system. Here's the list of equipment we plan to use:
- 2x EV ZLX12P
- 1x FBT MAXX10SA
- notebook with MIDI controller (source of music)
- 2 or 5 channel mixer
- lightmaxx cls-3

I was wondering how powerful electrical generator should we get in order to make sure there won't be any problems? Where's the bottom end line in specifications? Could we actually damage the equipment if generator wouldn't output enough power?
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Re: How powerful generator is needed for this PA system

Postby dmills » Sun Aug 10, 2014 10:47 am

I figure about 5KVa should be safe, but you **MUST** use a set equipped with an AVR, the sort of thing you hire from your local builders tool hire place is NOT suitable.

The magic phrase when hiring such a machine is 'super silenced, entertainment grade', any of the better sort of generator hire places will know what you mean.

Even with super silenced set you will want it a reasonable distance away from the stage, so also hire some appropriate cable and a small distro to 13A sockets.

Regards, Dan.
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Re: How powerful generator is needed for this PA system

Postby Sam Spoons » Mon Aug 11, 2014 11:41 am

I have successfully used a 2 KVA suitcase genny (my Kippor IG2000P Inverter generator, a clone of Honda's EU2.0) to run a much bigger rig than yours (2xQSC K12s, 3xYamaha DXR10s Mackie DL1608 desk, Ashdown Superfly 500 watt bass head and an 18 watt valve guitar combo, I'll be doing the same again in a couple of weeks but with my EV sBa750 sub added to the rig). The genny never got off tick over and was quiet enough tucked behind the car about 10 metres from the stage. As Dan says don't consider a hire shop special (though I was forced to do that a couple of weeks ago and while it actually worked fine I'd prefer not to risk my expensive digital kit that way again). The only issue is with subs, if you need loads of sub bass I can't vouch for that. BTW The hire shop genny mentioned above was a budget 2.6KVA job and it ran a 6 piece covers band with a pair of K12s, two SRM350s, two Art subs and back line, the voltage stayed pretty stable at around 230 VAC and the current drawn didn't exceed 6A (so well within my Kippor's 7.8A) at any time. I'd have been perfectly happy running it off my Kippor, Inverter generators supply extremely stable voltage and frequency and are perfectly suitable for powering delicate equipment.

If the event is for a paying client I'd say go with Dan's suggestion but if it's a more informal gig consider a 2-3KVA inverter genny if you can hire one at a sensible (I.e. cheaper than a big diesel genny) cost.

Just one other point, some venues won't allow petrol on site so it has to be a diesel set.
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Re: How powerful generator is needed for this PA system

Postby Exalted Wombat » Mon Aug 11, 2014 6:01 pm

dmills wrote:Even with super silenced set you will want it a reasonable distance away from the stage, so also hire some appropriate cable and a small distro to 13A sockets.

You're probably stuck with having it quite close to the stage, else you'll have all sorts of extra complications feeding the power through audience-accessible areas.
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Re: How powerful generator is needed for this PA system

Postby mick.n » Mon Aug 11, 2014 6:41 pm

It was some years ago now, but i remember we played at an outdoor event (big massive tent) & i seem to remember something called "equipotential area" bonding stuff etc, etc.
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Re: How powerful generator is needed for this PA system

Postby dmills » Mon Aug 11, 2014 7:31 pm

Yep, applies if your supply is taken from a TN-C-S source (Like say most modern buildings), it is a pain in the arse. If going there, far better to opt for TT with an RCD and half a dozen spikes.

Unlikely to apply to a local generator which if setup for entertainment use will most likely be TN-S, or if a shonky piece of site junk may be IT or suchlike weirdness.

These codes are a UK thing, see BS7671 for details.

Nomenclature :

TN Earthed neutral
TT Earth return via the body of earth (Almost always needs an RCD to meet disconnect times).
-C common neutral and earth conductor
-S Separate neutral and earth conductor
IT Floating supply relative to earth.

Thus TN-C-S is the (very common in newer domestic installs) design whereby the transformer has an earthed neutral and the cable in the street has a single conductor that serves as both the neutral and the earth return (C) with these only being separated at the property (S).
The failure mode to worry about is a lost neutral connection in the 'C' part of the circuit at which point all connected metalwork rises to mains potential, not a problem as long as everything is cross bonded so it all comes up together, but big problem when you have taken a feed out into the garden for powering a wedding tent.

TN-S does not have this little issue, but requires much more copper as you add an extra wire to the suppliers arrangements, somewhat uncommon these days.

TT is mostly seen way out in the sticks, RCDs are almost mandatory because you generally cannot get the loop impedance low enough to blow a fuse in reasonable time.

Portable and mobile generating sets should probably be TN-S unless tiny and only running a single load where IT may be acceptable.

Regards, Dan.
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Re: How powerful generator is needed for this PA system

Postby Marjan Dobelsek » Fri Aug 15, 2014 9:49 pm

Maybe I could get Honda EU10i and EU20i, so I was thinking to power up 1x FBT MAXX10SA with EU10i and everything else with EU20i (2x EV ZLX12P, notebook and mixer). Lights are optional. Do you think that could work? Could there be any grounding issues?

In fact I could even power notebook and mixer with 12V to 230V inverter from accumulators. In that case, it would look like this:
EU10i: 1x FBT MAXX10SA
EU20i: 2x EV ZLX12P
1000 W 12-230V inverter from acc: notebook and mixer

What do you think guys? Is that combination rock-solid?
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Re: How powerful generator is needed for this PA system

Postby MarkOne » Sat Aug 16, 2014 12:25 pm

I'm no expert with gennys, but my college electrical engineering (albeit from sometime way back in the previous millennium) is telling me you would be in a world of hurt trying to run a system off two independent gennys, the AC wouldn't be in sync and you would certainly have to do something about common earthing.

You'd be much better off just getting a single unit that is rated correctly. IMO, of course.
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Re: How powerful generator is needed for this PA system

Postby Sam Spoons » Mon Aug 18, 2014 9:31 pm

+1, get just one genny or you'll run into problems. From what you say the the bigger Honda should do the job with ease (see my earlier post, I'll let you know if I can run all that plus the sub after the gig on Sunday :).
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Re: How powerful generator is needed for this PA system

Postby Sam Spoons » Tue Aug 26, 2014 10:26 am

The Band On The Beach gig went well on Saturday, the ebay genny (Kippor IG2000) coped with 1 EV sBa750 sub, 2 x QSC K12 tops, 3 x Yamaha DXR10 monitor wedges, Mackie DXR1608 mixer, 1 x 18watt valve guitar combo, 1 x Ashdown Superfly (500 watt) bass rig and 2 x LED PAR cans. The audience was around 400 and many commented favourably on the sound quality. Everything was miked with plenty of kick and bass in the sub. The icing on the cake was that we raised over £700 for the RNLI. Some pics here Band On The Beach pics
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Re: How powerful generator is needed for this PA system

Postby AdrianTatar » Wed Sep 03, 2014 1:45 pm

HY

The most important is to be a inverter generator, so you'll be sure not ruin the equipment. Power generators used in construction have voltage variations and are not good for your type of application.

2 pieces EV ZLX 12P consume max 250w
FBT MAXX 10SA 500w,
notebook with MIDI controller max 100w,
2 or 5 channel mixer max100w
and lightmaxx cls-3 (28*8w) 224w
total 1174w

Honda EU20i is ok.

All the best
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Re: How powerful generator is needed for this PA system

Postby Sam Spoons » Fri Sep 05, 2014 9:33 am

It doesn't have to be an inverter generators, they are are great but only go up to about 4KVA, above that you're into the realms of diesel gennys. Big shows/festivals use big diesel gennys and they supply clean mains power up to hundreds of KVA.
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Re: How powerful generator is needed for this PA system

Postby AdrianTatar » Fri Sep 05, 2014 11:59 am

Sam Spoons wrote:It doesn't have to be an inverter generators, they are are great but only go up to about 4KVA, above that you're into the realms of diesel gennys. Big shows/festivals use big diesel gennys and they supply clean mains power up to hundreds of KVA.

Hy

What u are saying is half true. If u are using a constant load is ok, but to my knowledge the music has a consumption that is oscillating, how well do a normal generator this ?

All the best
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Re: How powerful generator is needed for this PA system

Postby Sam Spoons » Fri Sep 05, 2014 1:02 pm

Absolutely fine provided the genny is properly voltage regulated (as pretty much all large sets are) we've been running festivals from them since Woodstock and before. Inverter generators are great for small rigs (see my earlier post) but can't supply the power for large events, the biggest inverter generator I'm aware of is the Honda EU4.0i at 4KVA. What I wouldn't do is run a modern PA rig off a cheap, low powered hire shop genny, they are designed to run building site equipment but not delicate stuff like computers or digital mixing desks.
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